1. Field of the Invention
The present invention relates generally to amorphous semiconductor devices and more specifically to contacts and interconnects for amorphous semiconductor devices formed on silicon substrates.
2. Description of the Prior Art
One of the concerns in amorphous semiconductor devices, be they threshold or memory devices, has been the proper selection of the contact materials. It it well known that these materials must be carefully selected to avoid contamination of the amorphous semiconductor material. Although aluminum is a well known conductor used especially with silicon substrates because of its low resistance and high adherence to silicon, it is generally unsatisfactory as a contact to amorphous semiconductor layers since the aluminum migrates into the amorphous material when current flows from the aluminum into the amorphous material. The problem of aluminum migration is overcome by using refractory materials such as molybdenum to isolate the aluminum from the amorphous material.
Although molybdenum provides a good isolating medium layer between the aluminum and the semiconductor material, molybdenum does not make ohmic contact with the silicon substrates. Prior devices generally used a thin layer of palladium silicide between the molybdenum and the silicon substrate to provide an ohmic contact. Molybdenum interconnects between the contact areas of the systems have proved to be unsatisfactory since they have such high sheet resistance. The high resistance has prevented the use of amorphous semiconductor devices at high speeds.
Thus, there exists a need for a contact interconnect system for amorphous semiconductor devices on a silicon substrate having low resistance, providing good adherence to the silicon substrate, preventing migration of the contacts into the amorphous layer, and providing ohmic contact to the silicon substrate.